[jax-rs-spec users] Re: What is the standard behavior when injecting property on a singleton resource class?

From: Grant G Yang <>
Date: Tue, 22 Jul 2014 13:05:50 +0800

Thank you Marek, I think that is sufficient for me to understand the
expected behavior.


From: Marek Potociar <>
Cc: Grant G Yang/China/IBM_at_IBMCN
Date: 07/21/2014 09:30 PM
Subject: Re: What is the standard behavior when injecting property on a
            singleton resource class?


(rerouting your request to and dropping the
JSR311 mailing lists via BCC.)

On 21 Jul 2014, at 14:56, Grant Yang <> wrote:

      Dear experts,

      When discussing the support of field / property injection, especially
      @Context injection, the spec document seems lack of details on the
      part of support singleton resource classes (either returned from
      Application.getSingletons() or annotated with @Singleton).

      1. The spec explicitly mentioned that for non-per-request resource
      classes, support of field / property injection is not supported, but
      saying "with the exception of @Context". However for @Context, there
      are also request scope values (UriInfo, Request, HttpHeaders,
      SecurityContext) and non-scope (Application, Providers,
      ResourceContext, Configuration) values. What is the expected way to
      handle these very request scope values per spec?

As defined in the spec, @Context supports injection of only a limited
enumerated set of JAX-RS interfaces. Since these are interfaces, in case of
request-scoped values into non-request scope injection points, delegate
proxies can be injected. These proxies can, of course, fail to provide
information when accessed from outside of a request scope.

      2. How many times the injection shall be done to a singleton resource
      class? I see in the latest javadoc of Application.getSingleton()
      saying "Fields and properties of returned instances are injected with
      their declared dependencies (see Context) by the runtime prior to
      use." While "prior to use" is not a good way to describe the
      behavior, as "prior to use on the first request" or "prior to use on
      every request". The implementation shall inject the value only once
      or every time a request comes by?

Ideally, injection into instance fields should happen only once, but the
JAX-RS spec does not define or enforce this behavior, IIRC.


      Actually when reading Jersey document I see Jersey already got some
      answer of above questions, but not as part of spec; therefore I
      wanted to get suggestions from you experts, on which part of complies
      to the spec, which part shall belong to Jersey implementation
      specified (but of course can be treated as best practice).

      Any comments/suggestions will be more than welcome. Thanks in

(image/gif attachment: graycol.gif)